In this work, we propose a method to synthesize vanadium (IV) 2-benzyli-dene-1-indanone derivatives, used to prepare film structures by thermal evaporation. The complexes possess high melting point allowing the using of vacuum deposition methods. All the samples were grown at room temperature (25 ℃) and low deposition rates (0.4 Å/s). The surface morphology and structure of the deposited films were studied by scanning electron microscopy (SEM) and spectroscopy dispersive energy (EDS). Optical absorption studies of the complex films were performed in the 200 - 1100 nm wavelength range. The Tauc band gap (Eg) of the thin films was determined from the ( αhν) 1/2 vs. hν plots for indirect transitions. The vanadium (IV) complex films show optical activation energies in the range of organic semiconductors. Multilayer nylon 11/vanadium indanone devices were fabricated using ITO and silver electrodes. The d.c. electrical properties of the device were also investigated. It was found that the temperature-dependent electric current in the structure showed a semiconductor behavior. At lower voltages below 7 V, the current density in the forward direction was found to obey an ohmic I-V relationship; for higher voltages above 7 V, the conduction was dominated by a space-charge-limited (SCLC) mechanism. The electrical activation energies (Ea) of the complexes were in the 2.17 - 2.31 eV range.
The use of organic semiconductors in the manufacture of electronic gadgets such as light-emitting diodes, rechargeable batteries, sensors, and electronic devices, has shown a rapid increase in recent years. The low cost of manufacturing organic semiconductors, easy manipulation of specific properties and their compatibility to relatively cheap substrates when they are deposited as thin films, are the main causes for this upsurge. Organic semiconductors also show excellent properties at relatively low temperatures such as high electroluminescence, good charge mobilities, and mechanical flexibility, among others. The main difference between or- ganic semiconductors compared with single atom inorganic semiconductors is the presence of separate molecules, which maintain most of their characteristics even in the solid-state form [
Under these circumstances, vanadium compounds can be exploited to produ- ce organic semiconductors, magnetic materials and display devices [
Preliminary results of the study of iron (III) complexes of 2-benzylidene-1- indanone derivatives thin films showed that the chemical differences between the substituents in the complexes and the structural variations did not have a great impact in the band gap value. Nevertheless, the metal arrangements during the thin film formation provided a glimpse on the optical properties of these compounds [
All reagents were obtained from commercial suppliers and used without further purification. The compounds were characterized by IR spectra, recorded on a Perkin-Elmer 283B or 1420 spectrophotometer, by the KBr technique. Melting points were obtained on a Melt-Temp II apparatus and are uncorrected. Nuclear magnetic resonance spectra were recorded with a Bruker AV 400 or JEOL Eclipse +300 spectrometer. Chemical shifts for the 1H NMR spectra were recorded in parts per million from tetramethylsilane with the solvent resonance as the internal standard (chloroform, δ = 7.25 ppm). Chemical shifts for the 13C NMR spectra were recorded in parts per million from tetramethylsilane using the central peak of CDCl3 (δ = 77.1 ppm) as the internal standard. Mass spectra were recorded with a JEOL JMSAX 505 HA spectrometer at 70 eV using the electronic impact (EI) and fast atom bombardment (FAB+) technique.
o-Phthalaldehyde was added to a cool sodium hydroxide (1.5 eq.) ethanolic solu- tion with 1 equivalent of acetophenone. The reaction mixture was stirred (around 450 rpm) at room temperature for approximately 3 hours and then poured into a mixture of ice and commercial hydrochloric acid (pH was adjusted to about 7). The resulting solid was filtered and in some cases purified by column chromatography using hexane/ethyl acetate (
Compound 1 (C16H12O2, M = 236 g/mol) was prepared starting from o-phthala- ldehyde (0.5 g, 3.7 mmol), acetophenone (0.48 g, 3.7 mmol) and NaOH (0.119 g, 2.98 mmol) and was obtained as a yellow solid, mp. 90˚C, (0.67g, 2.82 mmol, 75%). IR: ν 1604, 1564 cm−1. 1H NMR (300 MHz, CDCl3): δ = 15.067 (s, 1H, OH),
7.49, 7.5 (d, 1H, 1), 7.54 (dd, 1H, 2), 7.40 (dd, 1H, 3), 7.85 (d, 1H, 4), 7.91 (m, 1H, 10), 7.48 (m, 3H, 11, 12, 13), 7.91 (m, 1H, 14), 3.86 (sa, 2H, 15) ppm. 13C NMR (75 MHz, CDCl3): δ = 125.54 (C1), 133.27 (C2), 127.40 (C3), 123.36 (C4), 137.85 (C5), 195.70 (C6), 109.41 (C7), 170.79 (C8), 134.79 (C9), 128.07 (C10), 128.55 (C11), 131.21 (C12), 128.55 (C13), 128.07 (C14), 32.19 (C15), 148.51 (C16) ppm. MS (EI): m/z (%) = 236 (1.9%). HRMS (FAB+): calculated for C16H12O2: 237.0821. Found: 237.0823.
Compound 2 (C17H14O3, M = 266 g/mol) was prepared starting from o-phtha- laldehyde (0.5 g, 3.7 mmol), 4’-methoxyacetophenone (0.56 g, 3.7 mmol) and NaOH (0.119 g, 2.98 mmol) and was obtained as a yellow solid, mp. 112˚C - 114˚C, (0.7 g, 2.6 mmol, 71%). IR: ν 1601, 1566 cm−1. 1H NMR (300 MHz, CDCl3): δ = 15.33 (s, 1H, OH), 7.47 (d, 1H, 1), 7.51 (dd, 1H, 2), 7.37 (dd, 1H,3), 7.82 (d, 1H, 4), 7.89 (d, 2H, 10, 14), 6.95 (d, 2H, 11, 13), 3.82 (s, 2H, 15), 3.83 (s, 3H, 17) ppm. 13C NMR (75 MHz, CDCl3): δ = 125.37 (C1), 132.85 (C2), 127.23 (C3), 123.03 (C4), 137.87 (C5), 194.84 (C6), 108.32 (C7), 170.04 (C8), 127.00 (C9), 129.99 (C10), 113.88 (C11), 162.06 (C12), 113.88 (C13), 129.99 (C14), 32.45 (C15), 148.09 (C16), 55.30 (C17) ppm. MS (EI): m/z (%) = 266 (15%). HRMS (FAB+): calculated for C17H14O3: 267.1021. Found: 267.1023.
A solution of EtOH with 2-benzylidene-1-indanones derivatives and vanadium (V) oxide V2O5 was heated under reflux during one night. The resulting greenish blue solid was filtered and crystallized in dichloromethane/hexane solution (Fig- ure 2).
Compound 1a (C32H22O5V, M = 537 g/mol) was prepared starting from 1 (0.5 g, 2.1 mmol) and V2O5 (0.2 g, 1.1 mmol) in EtOH and was obtained as a greenish blue solid, mp. 272˚C - 274˚C. IR: ν 3060, 1589, 1552. MS (FAB+): m/z (%) = 538 (10%). HRMS (FAB+): calculated for C32H22O5V [M+]: 537.0907. Found: 534.0915.
Compound 2a (C34H26O7V, M = 597 g/mol) was prepared starting from 2 (0.5g, 1.9 mmol) and V2O5 (0.17g, 0.9 mmol) in ETOH and was obtained as a green solid, mp. 270˚C - 272˚C. IR: ν 3056, 1595, 1544. MS (FAB+): m/z (%) = 597 (100%). HRMS (FAB+): calculated for C34H26O7V [M+]: 537.1112. Found: 534.1118.
Thin film deposition of the metal complex of 2-benzylidene-1-indanones derivatives was carried out by vacuum thermal evaporation. The material was deposited onto Corning glass and (100) single-crystalline silicon (c-Si) 200 Ω-cm wafers. The substrate temperatures were kept at 298 K during deposition. The evaporation source was a molybdenum boat and the temperature through the molybdenum boat was slowly increased to 498 K. The pressure in the vacuum chamber before the film deposition was 1 × 10−5 torr and the evaporation rate was 0.4 Å/s. IR measurements were obtained with a Nicolet iS5-FT spectrophotometer, using silicon flakes as a substrate for the thin films. For SEM, a JEOL field emission electron microscope (JSM7800F) coupled to an Aztec microanalysis system and operated at a voltage of 20 kV and a focal distance of 20 mm, using thin films on a Corning glass substrate, was employed. Ultraviolet-visible spectroscopy was carried out in a Unicam spectrophotometer; model UV300, with a Corning glass. The device consisting of V(IV) 2-benzylidene-1-indanones derivative particles embedded in nylon 11 matrix was prepared by consecutive evaporation of the polymer and the complex, and then with a heat treatment. The nylon 11 matrix film was prepared onto Corning glass substrates with a contact conductor of indium tin oxide (ITO) by a vapor deposition of a nylon 11 pellet using a double vacuum chamber with a diffusion pump and a special tantalum crucible. The pressure in the vacuum chamber before the film deposition was (1 × 10−6 Torr) and the evaporation rate was (70 Å/s). After the vapor deposition, in order to introduce the vanadium complex particles into the nylon 11 matrix, a heat-treatment at 393 K for 10 min was applied. The electric conductivity of the device was studied by means of a four- point probe; for these measurements, the substrates are ITO coated glasses with si- lver strips acting as electrodes. Electric characterization was performed with a pro- grammable voltage source, an auto-ranging pico-ammeter Keithley 4200-SCS- PK1, a sensing station with lighting controller circuit and a sensing station with temperature controller circuit Next Robotix.
As far we know, there is not a net influence of the different moiety groups in these ligands. We used our methodology to synthesized 2-benzylidene-1-indanone derivatives to obtain compounds 1a and 2a [
Compound | IR characteristic bands | |||
---|---|---|---|---|
ν (C=O) | ν (C-O) | ν (V=O) | ν (C-O-V) | |
1a (pellet) | 1588 | 1551 | 970 | 1327 |
1a (thin film) | 1589 | 1554 | 998 | 1328 |
2a (pellet) | 1594 | 1545 | 986 | 1327 |
2a (thin film) | 1600 | 1550 | 992 | 1328 |
[
In order to promote a semiconductor behavior with the vanadium complexes, it was necessary to guarantee the chemical stability of the molecule at high temperatures, since the electronic delocalization and the mobility of the charge carriers between the coordination sphere of the vanadium atom and the ligand, is crucial. In order to complement the IR Spectroscopy results and to verify the metallic complexes stability after evaporation, an additional EDS analysis was performed.
To know the homogeneity and morphology of the films, SEM images from samples deposited on monocrystalline silicon were obtained. The SEM micro-
graphs in
The UV-vis spectra of vanadium film complexes of 2-benzylidene-1-indano-
ne derivatives were acquired in Corning glass substrates at room temperature. The electronic spectral data of the thin films is given in
Thin Film | UV-Vis Data λ (nm) | Film Thickness (Å) | Indirect Optical |
---|---|---|---|
1a | 272, 379, 406 | 40 | 2.7 |
2a | 226, 271, 376, 386, 391 | 1527 | 2.6 |
and 2.7 eV. This variation is minimal and is mainly due to the change of radical and its polarity in the vanadium complexes 1a and 2a.
By comparing the behavior to vanadium complexes in
As mentioned above, in order to evaluate the electrical properties of the thin films for their use in optoelectronics, a multilayer glass/ITO/nylon 11/1a complex/Ag device was fabricated by using the thermal relaxation technique. One crucial factor that affects the operation of these devices is the protection of the organic semiconductor against harsh environmental conditions [
The conducting behavior of vanadium complex was evaluated by increasing the temperature, with the purpose to complement the information regarding its semiconducting behavior and its usage for optoelectronic devices. In one hand,
Additionally, electrons can hop from the metallic atom to the 2-benzylidene-1- indanone ligand. A plot of ln σ versus 1/T yields a straight line which slope can be used to determine the thermal activation energies (Ea) of the vanadium films [
New vanadium complexes were synthesized with moderated yields with an easy and clean reaction and were also characterized. Due to their physical properties, vanadium indanone thin films were deposited by thermal vacuum evaporation. Thin film morphology seems to depend on the molecular structure of the ligand around de vanadium atom; polarity in the radical of ligand is a decisive factor for the morphology and thickness of the formed film. The optical band gap was calculated and the values were found to be around 2.7 eV for indirect transitions. Differences in the GAP values were possibly related to factors such as the radical in the molecule, differences in size of the particles in the film and the molecular overlap of the thin film. 2-benzylidene-1-indanone vanadiummultilayer structure involving conductor-semiconductor interfaces has been fabricated using ITO and silver contact materials among others. The incidence radiation with different wavelengths on the device produced an ohmic behavior at values lower than 7 V, while an SCLC mechanism at values higher than 7 V was evidence. The effect of temperature on the conductivity was also evaluated and showed typical semiconducting characteristics. The existence of trap levels is confirmed by the presence of three linear portions in the ln σ vs. 1/T plots. From this work, ITO/nylon 11/vanadiumindanone/Agarrangements show potentially useful electronic properties that may be employed in the production of electronic devices for optoelectronic applications.
The authors wish to thank the technical assistance of Rocío Patiño, Luis Velasco, Javier Pérez, Isabel Uribe, and also C. González Normandía. The authors gratefully acknowledge the financial support of CONACYT Project 127796 and DGAPA- PAPIIT Project IN207414. We would also like to thank CONACYT for the Ph.D. grant extended to M. L. G.
Lozano-González, M., Sánchez-Vergara, M.E., Alvarado-Bel- trán, I., Leyva-Esqueda, M., Rivera, M. and Álvarez-Toledano, C. (2017) Synthesis and Evaluation of the Semiconductor Behavior in Vanadium Indanone Derivatives Thin Films. Advances in Materials Physics and Chemistry, 7, 70-83. https://doi.org/10.4236/ampc.2017.72007